xxiv SUPPLEMENT TO THE CRAG MOLLUSCA. 



The Great Chalky Clay, or Upper Glacial (No. 9). 



This wide-spread unstratified deposit extends over the eastern and the east central 

 counties, and is there wholly unfossiliferoiis. In the parts traversed by the sections it is 

 mostly of no great thickness, owing apparently to denudation ; but further from the 

 coast, and away from the main valleys, its thickness is more considerable, amounting in 

 the west of Suffolk to as much as 1.20 feet, 1 and in Cambridgeshire to still more. Where 

 it does not descend, as it often does, in a plunge, but rests evenly on the Middle Glacial 

 sand, as around \Yoodbridge and in Sections T and U, this clay not unfrequently passes 

 down into that sand by a passage bed consisting of a few feet of the clay which becomes 

 more sandy downwards, until it shades off into the subjacent sand. In other places it lies 

 evenly upon the sand in a conformable manner without any such passage bed ; and there 

 can be little question that the succession was effected by tranquil deposition, uninterrupted 

 by any change of conditions other than those which produced a new kind of sediment. This 

 clay all may admit to be the result of the degradation of the Cretaceous, Oolitic, and Liassic 

 districts by land ice — the moraine prof onde of the great enveloping ice sheet of the Upper 

 Glacial period; but no one can look at the even way in which it overlies the sand in 

 Kessingl&nd and Hopton Cliffs (Sections T and U) without being convinced that it could 

 not have been so placed by the action of land ice, since this could not have failed to crumple 

 up and distort those sands, just as the intruding bergs bringing the marl masses churned up 

 the contorted drift. Sectiou P shows what an ice plough of the period of the clay Xo. 9 

 would accomplish. The Crag and the overlying sand, 8, of this section appear on one side 

 of the cutting at the East Suffolk Railway Junction ; but in the short space of the width 

 of the cutting they are cut off so entirely, that the opposite side presents nothing but a 

 churn up of sand and London clay ; while a piece of the Red Crag thus ploughed out 

 has been left two miles off, at a high level, in a mass of gravel about the junction of the 

 Middle Glacial sand with the chalky clay, and is exposed in a pit south of the " Sparrows 

 nest." If this be the result of the grounding of an ice island, as we cannot doubt it was, 

 how much of the sand of Hopton and Kessingland Cliffs would have been left under the 

 pressure of the land-ice sheet itself ? Nevertheless this clay, not only in these cliffs, but 

 all over East Anglia, is quite as unstratified as is that of Scotland and the north of 

 England, and it is everywhere, except on the Yorkshire coast, quite as destitute of organic 

 remains. 



The species given in the Crag Mollusca and its Supplement from the Upper Glacial 

 formation are from the Bridlington bed, the age of which appears to us to be posterior to 

 that of the great chalky clay of East Anglia (No. 9) ; the bed occurring in a continuation of 



1 Tbis -was the total thickness in the cutting and contractor's well beneath it at Horseheath on the 

 borders of Cambridgeshire and Suffolk. The cutting: and well at Old North Road Station of the Cambridge 

 and Oxford Railway showed this clav there to be about 160 feet in thickness. 



